NPR Blogs

How Tall Is The Washington Monument? Surveyors Take To The Top

By Andrew Prince

Published November 8, 2013 at 12:31 PM EST

National Geodetic Survey crew members Roy Anderson, left, and Steve Breidenbach set up survey equipment used to measure the height of the Washington Monument.

The National Geodetic Survey doesn't often get the opportunity to take detailed measurements of the massive stone obelisk that sits in the middle of Washington, D.C.

Don Breidenbach, left, and Kendall Fancher take measurements of at the very top of the Washington Monument.

But a 2011 earthquake in nearby Mineral, Va., damaged the Washington Monument enough that to repair it, the tower had to be wrapped in scaffolding. That gave surveyors access to the very top of the structure.

With $15 million in repairs nearing completion, the government office in charge of knowing the precise latitude, longitude and elevation of things all across the country had a prime opportunity to check whether the monument still clocks in at its official height of 555 feet, 5 1/8 inches.

Ben Sherman of the says the latest survey of the monument's height was completed in 1999 and that the current work is part of an ongoing historical survey, which began in 1901.

Located on the National Mall, the Washington Monument opened to the public in October 1888. Sherman says much of the land the National Mall sits on is actually landfill covering the Tiber Creek, which ran through Washington and drained into the Potomac River. "So there is the possibility of land sinking over time," Sherman says.

A "triangulation party" measures from the top of the Washington Monument on Nov. 19, 1934. Scaffolding was set up to clean the structure.

That's what happened at the nearby Jefferson Memorial, where in 2010 workers had to drive new pilings down into the bedrock to shore up a sinking seawall.

To see if there's any movement of the Washington Monument, the survey team climbed to the top of the scaffolding last week to put up some special sensors. "We were able to build an adapter that fits on top of the monument," Sherman says.

The team outfitted the top of the monument with GPS equipment and special sensors and "collected data from satellite and ground-based laser readings."

Sherman says they'll spend the next two months or so crunching the numbers and comparing data from the survey done in 1999.

"We always want to take advantage of opportunities like this," he says. Measurements like these "aid in the preservation of monuments and get an early read on changes, helping us mitigate any potential problems."

When the analysis is complete, they'll announce a new certified height. But Sherman cautions: "Very likely, it won't change."